Fetal Pig Dissection

Fetal Pig Dissection Objective In this exercise you will examine the organization of the many body systems studied this semester in the context of a single specimen, the fetal pig. Be sure to identify the major organs as you explore the extent of each system As you encounter each structure, discuss its function and interactions with surrounding structures with your lab partners Recommendations: Carefully follow the directions Read the description of each incision and understand it prior to beginning All students must wear goggles Each group should have a • Directions reader • Recorder • Dissector(s) • All students handling the specimen must wear gloves Rotate roles for each section of the dissection • Record who is responsible for each role in the response PowerPoint Use the scissors for most incisions unless otherwise instructed Clean-up at the end of each day Dispose of lab discards in the large trash can 2 Clean dissection pan and instruments and leave the to dry at the side of the room (you will use the same trays again the next day) 5 Wash your hands! Place your pig into the plastic bag provided 1 • Expel excess air from the bag and tie it shut • Write your group name and class time on the bag 3 Save your response PowerPoint!! 4 Clean table tops! About the Fetal Pigs The fetal pigs are unborn animals. In processing the sows (mature female swine) for meat, the uterine horns often reveal unborn litters. These are removed and made available for biological study. Note the umbilical cord of your specimen. There are usually 7 to 12 young in a single litter. Part A: Observing the External Features of the Fetal Pig The specimens which you will dissect in the laboratory are full term pigs. The period of gestation or development is 112-115 days and there are on the average 7-12 offspring in a litter. The age of the fetus can be approximated by measuring the length of the body. Length of Fetus (cm) Approximate age (days) 1.1 21 1.7 35 2.8 49 4.0 56 22.0 100 30 Full term 112-115 Part A: Observing the External Features of the Fetal Pig • Body: – The body is divided into a head, neck, body (divided into thorax and abdomen) and tail – Notice the umbilical cord arising from the ventral portion of the abdomen. • Label the following areas of the pig diagram on slide 3 of answer ppt: – – – – – – – – – – – – Dorsal surface Ventral surface Anterior end Posterior end Head Neck Thorax Abdomen Tail Forelimb Hindlimb Umbilical cord Part A: Observing the External Features of the Fetal Pig • Examine the fetal pig and locate the external features discussed below. – Two rows of nipples of mammary glands are present on the ventral abdominal surface of both males and females. Mammary glands later develop only in maturing females. – Umbilical cord: Make a transverse cut through the umbilical cord and examine the cut end. Locate the two umbilical arteries that carry blood from the fetal pig to the placenta, and the single umbilical vein that delivers nutrient-rich blood back to the fetal pig. • Determine the sex of your specimen (view diagrams on next slide) – Female: The urogenital opening in the female is immediately ventral to the anus and has a small genital papilla marking its location. – Male: The scrotal sac is ventral to the anus and a urogenital opening is just posterior to the umbilical cord. Male vs. Female Male Female Part A: Observing the External Features of the Fetal Pig Positioning the pig for dissection Place the fetal pig on a dissecting tray ventral (belly) side up. Use two or three rubber bands to tie the right hind leg around the ankle. Run the rubber bands around the underside of the tray and tie the left hind leg. Repeat for the forelegs. Part A: Observing the External Features of the Fetal Pig • HEAD AND NECK • To expose the structures of the mouth and pharynx, start by inserting a pair of scissors in the angle of the lips on one side of the head and cut posteriorly through the cheek. • Open the mouth as you make your cut and follow the curvature of the tongue to avoid cutting the roof of the mouth. • Hold down the epiglottis and surrounding tissue and continue your incision dorsal to it and on into the opening of the esophagus. • Now, repeat the procedure on the other side so that the lower jaw can be pulled down to expose the structures of the mouth and pharynx as shown on the next slide. Part B: The respiratory system • Your pig should be on its dorsal side, leaving the neck well exposed. • Carefully, slice open the skin in your pig’s throat from hairy chin to below the rib cage using scissors. • You must cut shallow or you will cut into the organs that you are trying to find. Locate all of the organs in the throat before you proceed to the next step. • Carefully peel back skin from the rib cage so you can locate the sternum, diaphragm and rib cage. Cut away the muscle and fat so you can see the ribs. DO NOT cut through the cartilage of the rib cage yet. • Then, open the thoracic cavity, using scissors to cut through the bone. The bones are soft therefore, when cutting through them be careful not to cut too deeply or you will damage the heart and lungs. Find the bottom of the rib cage and cut through the ribs moving up along the forelimbs. Fold the rib cage back and cut off the top. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Part B: The respiratory system Thymus Thyroid Pleural membrane Diaphragm Lungs Bronchi Trachea Esophagus Larynx Heart (does not show due to bronchi in the center of chest) Part B: The respiratory system • Beginning at the top of the stomach, trace the esophagus as it passes through the diaphragm and under the heart. At the anterior end of the esophagus on the ventral side is the trachea. Notice the rings of cartilage that surrounds the trachea. These rings give the trachea the appearance of a vacuum cleaner hose. Trace the trachea to the point at which it branches to each lung. • Continue the dissection of the neck anteriorly to find an enlarged area of cartilage. This is the larynx, often called the voice box. At the top of the trachea is the epiglottis, which you located when observing the mouth structures Part B: The respiratory system Take a picture of the dissected pig and label the following structures: –Diaphragm –Right and Left Lungs –Larynx –Trachea –Esophagus Part C: The cardiovascular system This section of the dissection is more difficult and requires a light and delicate touch. Remember: Arteries are injected with Red paint, Veins are injected with Blue. Part C: The cardiovascular system • Carefully dissect around the heart, picking away at the connective tissue between the blood vessels. • Locate the pulmonary artery, on the ventral side of the heart, as it leaves the right atrium. • The aorta, the largest and most important artery, can be found just beneath the pulmonary artery as it leaves the left ventricle. • Very careful dissection will allow you to find the ductus arteriosus, a short connecting vessel that functions in the fetus to shunt blood from the pulmonary artery directly to the aorta. This vessel allows most of the blood to bypass the lungs. Part C: The cardiovascular system • Study the heart, major veins, and major arteries by carefully removing tissue as necessary to expose the vessels. This is best done by separating tissues with a blunt probe and by picking away connective tissue (CT) from the blood vessels with forceps. • In a fetus, the placenta is the source of oxygen and nutrients, and also removes metabolic wastes from the blood. The lungs, digestive tract, and kidneys are nonfunctional. Circulatory adaptations to this condition make the circulation of blood in the fetus quite different from your study of the adult cardiovascular system. Part C: The cardiovascular system • Identify the following structures using the illustration as reference: – Heart: carefully cut away the pericardial sac from heart and great vessels • locate atria, ventricles, coronary vessels – Anterior vena cava: returns blood from head, neck, and forelegs to right atrium – Posterior vena cava: returns blood from regions posterior to heart to right atrium – Pulmonary artery (trunk): carries blood from right ventricle – Aorta: carries blood from left ventricle – Umbilical vein: carries blood rich in oxygen and nutrients from placenta to fetus – Ductus venosus: segment of umbilical vein going to liver and on to posterior vena cava carrying blood rich in placental oxygen and nutrients – Ductus arteriosus: carries blood from pulmonary trunk to aorta (bypassing the non-functional lungs) • white and underneath apex of heart – Umbilical arteries: carries waste-laden blood from pelvic region to placenta for disposal Part C: The cardiovascular system After locating the major arteries and veins, carefully cut through the major vessels and remove the heart. Leave stubs of the vessels on the heart and identify them. Take a picture of the heart and label the following: – Left and right atria – Left and right ventricles – Aorta (if visible) – Vena cava – Pulmonary trunk Part C: The cardiovascular system Part D: The Digestive System • First incision • Carefully cutting through only the skin with scissors reveals the underlying abdominal muscles. • You can begin to see the dark liver underneath the shiny, transparent peritoneal membrane. • Follow the large vein at the base of the umbilical cord. • Now, cut the vein so that the flap of skin with the umbilical cord can be turned back. (See next slide) Part D: The Digestive System • Further incisions will reveal the abdominal cavity encased by the shiny membranes. • Most of the digestive, excretory and reproductive organs reside in this cavity, along with organs from other systems Part D: The Digestive System • Cutting through the transparent membrane gives access to some of the internal abdominal organs. • The cavity is dominated by the liver (large, brown organ at anterior of cavity) and the small intestine, but the large intestine may not be visible. • In the image, the abdominal wall to the left and right of the midline incisions and the umbilical region have been "reflected" (pulled aside to show beneath). • The peritoneal membrane lining the inside of the abdominal wall appears shiny when wet. Part D: The Digestive System • With the following diagram – locate each of your pig’s organs in the digestive system. Remember the diagram has organs moved around to “see” other organs anterior to the cut or organs. You may need to carefully move your organs around to find everything. • Find the large five-lobed liver at the anterior end of the abdominal cavity. Under the liver is the stomach, a large pouch-like organ with two parts. The large anterior end is the cardiac stomach and the smaller end is the pyloric stomach. The point at which the stomach and small intestines meet is called the pyloric sphincter. Appendix Part D: Digestive System Take a picture and label the: – Liver – Large intestine – Small intestine – Stomach – Spleen – Gall bladder Part D: The Digestive System • Observe the dome shaped muscular wall at the most anterior end of the abdominal cavity just above the liver. This is the diaphragm. • Embedded on the underside of the right central lobe of the liver is the greenish gall bladder. Locate it, then find, and trace the bile duct, a small, tube-like structure that is attached to the gall bladder. Directly below the gall bladder, on the underside of the stomach, you will find a granular-looking organ, the pancreas. Both the gall bladder and the pancreas release enzymes through a duct into the small intestines to aid in digestion. Attached to the left edge of the stomach is a reddish smooth organ – the spleen. Part E: The Nervous System • The brain has three main parts, the cerebrum, the cerebellum, and the brain stem. The brain is divided into regions that control specific functions. – THE CEREBRUM: Frontal Lobe controls Behavior, Abstract thought processes, Problem solving, Attention, Creative thought, Some emotion, Intellect, Reflection, Judgment, Initiative, Inhibition, Coordination of movements , Generalized and mass movements, Some eye movements, Sense of smell, Muscle movements, Skilled movements, Some motor skills, Physical reaction, Libido. Occipital Lobe controls Vision & Reading. The Parietal Lobe controls Sense of touch (tactile sensation), Appreciation of form through touch (stereognosis), Response to internal stimuli (proprioception), Sensory combination and comprehension, some language and reading functions, some visual functions. The Temporal Lobe controls Auditory memories, Some hearing, Visual memories, Some vision pathways, Other memory, Music, Fear, Some language, Some speech, Some behavior and emotions, Sense of identity • Right Hemisphere (the representational hemisphere) controls the left side of the body Left Hemisphere (the categorical hemisphere) controls the right side of the body – THE CEREBELLUM controls balance, posture, cardiac, respiratory, and vasomotor centers. – THE BRAIN STEM controls Motor and sensory pathway to body and face, Vital centers. Part E: The Nervous System • Your pig should now be dorsal side up. • Remove the skin and muscle from the head and carefully expose the skull. • With a pair of scissors, poke a small hole to the anterior portion of the skull directly behind the pinnae (ears). Then continue cutting around the skull to remove the skull cap. – The covering, called the meninges, and the tougher, outer covering, called the dura mater, must be removed in order to see the brain. • Observe its contours and convolutions. CAUTION: the brains of the fetal pig are very soft and fragile. They will crush and crumble easily. Use extreme caution when removing the brain in order to see the sections of the brain. Part E: The Nervous System • The largest portion of the brain is the cerebrum. It is composed of 2 hemispheres, separated in the mid-line by a deep longitudinal fissure. • The cerebral hemispheres have sections called the frontal, temporal, occipital and parietal lobes overlaying the bone regions. The cerebrum can be described as a center of higher consciousness and thought. Behind the cerebrum is the cerebellum with its many tiny gyri and sulci. Part E: The Nervous System • Locate the regions on your pig brain {or another’s if you have brain damage} • Take a Picture of the Pig Brain and Label the – Cerebrum – Cerebellum – Spinal Chord – Longitudinal fissure • Carefully attempt to find your pig’s spinal cord and it’s attachment to the skull and brain cavity. Trace this down the length of your pig. Clean-up 1 Please dispose of all biological materials in the large trashcan. 2 Clean pan and all utensils in hot, soapy water. 3 Clean desk and clean hands thoroughly.